The present invention pertains to a rotational control apparatus and, more particularly, a splineless rotational control apparatus adapted for use in selectively controlling the transmission of rotational forces between first and second relatively rotatable members, and specifically in the preferred form to a frictional clutching device for driving a fan.
When it is desired to intermittently transmit rotational forces from one rotatable component to another, it is commonplace to interconnect the components with a clutch and then to selectively activate and de-activate the clutch as needed. Known clutch arrangements can be controlled using electrical, mechanical, pneumatic or hydraulic based actuation systems. Each of these actuation systems typically function by applying an axial load on a coupling element, generally constituted by either one of the rotatable components or a separate part, to create some relative axial shifting between the coupling element and one of the rotatable components in order to drivingly interconnect the two rotatable components.
In cases where a separate coupling element is utilized, the coupling element is usually drivingly connected with one of the rotatable components through a spline connection. With this arrangement, the coupling element can be readily shifted in the axial direction while still maintaining a drive connection with the respective rotatable component. The major disadvantage associated with this type of clutch is that the splines represent a high wear item and require expensive machining. Obviously, as the spline connection deteriorates, the entire function of the clutch is adversely affected and maintenance is required. Furthermore, the need for a lubricant, such as grease, is present.
In fluid actuated systems, the coupling element is almost invariably constituted by an annular piston. Typically, the piston will be acted upon by at least one spring which biases the piston towards one of an activated or de-activated position. When the two rotatable components are to be interconnected, fluid pressure acts on a side surface of the piston, opposite to that of the spring, to cause the piston to be axially shifted. Since the axial shifting force generated by the fluid is equal to the pressure of the fluid times the associated surface area of the piston, the surface area of the piston has a direct bearing on the level of force that can be developed. However, clutch pistons of this type typically have small surface areas, especially in the case of annular pistons which are positioned around hubs or the like. Correspondingly, these clutches have relatively low engagement and disengagement forces associated therewith.
Another problem recognized in this art concerns the transmission of loads through bearings. It is often found in the art of rotational control devices that rather high loads, particularly axial loads, are placed on bearing units arranged between relatively rotatable members. This high axial loading often results in fatigue failure of the bearings, thereby requiring the bearings to be periodically replaced.
Based on these and other recognized problems in the art, there exists the need for a rotational control device which avoids the use of a spline connection, enables a relatively high engagement or disengagement force to be developed and limits the degree of axial loading placed upon bearings therein.